U.S. patent application number 14/362067 was filed with the patent office on 2014-10-02 for method for measuring a wireless communication state in a wireless access system, and apparatus therefor.
This patent application is currently assigned to LG Electronics Inc.. The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Hanbyul Seo.
Application Number | 20140293953 14/362067 |
Document ID | / |
Family ID | 48668834 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140293953 |
Kind Code |
A1 |
Seo; Hanbyul |
October 2, 2014 |
METHOD FOR MEASURING A WIRELESS COMMUNICATION STATE IN A WIRELESS
ACCESS SYSTEM, AND APPARATUS THEREFOR
Abstract
Disclosed is a method for measuring a wireless communication
state in a wireless access system that supports an environment in
which the amount of an uplink resource and the amount of a downlink
resource dynamically change. Also disclosed is an apparatus for the
method. More particularly, the method comprises the steps of:
transmitting information on a resource to be measured to user
equipment; transmitting a reference signal to the user equipment;
and receiving, from the user equipment, the result of measurement
performed on the resource using the reference signal, wherein the
resource to be measured is determined by considering whether the
same resource is used for downlink or for uplink in a neighboring
base station.
Inventors: |
Seo; Hanbyul; (Anyang-si,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Assignee: |
LG Electronics Inc.
Seoul
KR
|
Family ID: |
48668834 |
Appl. No.: |
14/362067 |
Filed: |
December 21, 2012 |
PCT Filed: |
December 21, 2012 |
PCT NO: |
PCT/KR2012/011254 |
371 Date: |
May 30, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61579635 |
Dec 22, 2011 |
|
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04W 24/10 20130101;
H04L 5/0007 20130101; H04J 11/005 20130101; H04L 5/0073 20130101;
H04L 5/0048 20130101 |
Class at
Publication: |
370/329 |
International
Class: |
H04L 5/00 20060101
H04L005/00; H04W 24/10 20060101 H04W024/10 |
Claims
1. A method for supporting measurement of a user equipment (UE) in
a wireless access system for supporting an environment in which
amounts of uplink (UL) and downlink (DL) resources are dynamically
changed, the method comprising: transmitting information about
measurement resource to the UE; transmitting a reference signal to
the UE; and receiving a result of the measurement using the
reference signal in the measurement resource, from the UE, wherein
the measurement resource is determined based on whether a same
resource is used for DL or UL in an adjacent eNB.
2. The method of claim 1, wherein the measurement resource is
configured only in a subframe used for DL transmission by the
adjacent eNB.
3. The method of claim 1, further comprising transmitting
indication information indicating that the measurement resource is
valid when the measurement resource is configured as UL
resource.
4. The method of claim 1, wherein: the measurement resource is
divided into first measurement resource and second measurement
resource; the first measurement resource is configured only in a
subframe used for DL transmission by the adjacent eNB; and the
second measurement resource is configured only in a subframe used
for UL transmission by the adjacent eNB.
5. The method of claim 1, wherein the measurement comprises at
least one of reference signal received power (RSRP) measurement,
reference signal received quality (RSRQ) measurement, received
signal strength indicator (RSSI) measurement, and radio link
monitoring (RLM) measurement.
6. The method of claim 5, wherein: the RSRP is measured only in DL
resource; and the RSSI is measured only in UL resource used for DL
transmission.
7. The method of claim 5, wherein, in a case of the RSSI
measurement, a result of the measurement comprises distribution
information of measured RSSI values measured over a plurality of
predetermined subframes.
8. The method of claim 7, wherein the distribution information
comprises at least one of maximum and minimum of RSSI values
measured over a plurality of predetermined subframes, a frequency
at which RSSI that is equal to or more than a predetermined
threshold or is equal to or less than the predetermined threshold
is measured over the plural predetermined subframes, information of
a subframe in which the RSSI that is equal to or more than a
predetermined threshold or is equal to or less than the
predetermined threshold is measured over the plural predetermined
subframes, an average value of measured RSSI values that are equal
to or more than a predetermined threshold or equal to or less than
the predetermined threshold over the plural predetermined
subframes, an measured RSSI value corresponding to predetermined
top or low percentage among measured RSSI values measured over the
plural predetermined subframes, and an average value of measured
RSSI values corresponding to predetermined top or low percentage
among measured RSSI values measured over the plural predetermined
subframes.
9. A method of performing measurement in a wireless access system
for supporting an environment in which amounts of uplink (UL) and
downlink (DL) resources are dynamically changed, the method
performed by a mobile station and comprising: receiving information
about measurement resource from an eNB; receiving a reference
signal from the eNB; performing measurement using the reference
signal in the measurement resource; and transmitting a result of
the measurement to the eNB, wherein the measurement resource is
determined based on whether a same resource is used for DL or UL in
an adjacent eNB.
10. The method of claim 9, wherein the measurement resource is
configured only in a subframe used for DL transmission by the
adjacent eNB.
11. The method of claim 9, further comprising transmitting
indication information indicating that the measurement resource is
valid when the measurement resource is configured as UL
resource.
12. The method of claim 9, wherein: the measurement resource is
divided into first measurement resource and second measurement
resource; the first measurement resource is configured only in a
subframe used for DL transmission by the adjacent eNB; and the
second measurement resource is configured only in a subframe used
for UL transmission by the adjacent eNB.
13. The method of claim 9, wherein the measurement comprises at
least one of reference signal received power (RSRP) measurement,
reference signal received quality (RSRQ) measurement, received
signal strength indicator (RSSI) measurement, and radio link
monitoring (RLM) measurement.
14. The method of claim 13, wherein: the RSRP is measured only in
DL resource; and the RSSI is measured only in UL resource used for
DL transmission.
15. The method of claim 13, wherein, in a case of the RSSI
measurement, a result of the measurement comprises distribution
information of measured RSSI values measured over a plurality of
predetermined subframes.
16. The method of claim 15, wherein the distribution information
comprises at least one of maximum and minimum of RSSI values
measured over a plurality of predetermined subframes, a frequency
at which RSSI that is equal to or more than a predetermined
threshold or is equal to or less than the predetermined threshold
is measured over the plural predetermined subframes, information of
a subframe in which the RSSI that is equal to or more than a
predetermined threshold or is equal to or less than the
predetermined threshold is measured over the plural predetermined
subframes, an average value of measured RSSI values that are equal
to or more than a predetermined threshold or equal to or less than
the predetermined threshold over the plural predetermined
subframes, an measured RSSI value corresponding to predetermined
top or low percentage among measured RSSI values measured over the
plural predetermined subframes, and an average value of measured
RSSI values corresponding to predetermined top or low percentage
among measured RSSI values measured over the plural predetermined
subframes.
17. An eNB for supporting measurement of a user equipment (UE) in a
wireless access system for supporting an environment in which
amounts of uplink (UL) and downlink (DL) resources are dynamically
changed, the eNB comprising: a radio frequency (RF) unit for
transmitting and receiving a radio signal; and a processor which is
configured to: transmit information about measurement resource to
the UE; transmit a reference signal to the UE; and receive a result
of the measurement using the reference signal in the measurement
resource, from the UE, wherein the measurement resource is
determined based on whether a same resource is used for DL or UL in
an adjacent eNB.
18. A user equipment (UE) for performing measurement in a wireless
access system for supporting an environment in which amounts of
uplink (UL) and downlink (DL) resources are dynamically changed,
the UE comprising: a radio frequency (RF) unit for transmitting and
receiving a radio signal; and a processor which is configured to:
receive information about measurement resource from an eNB; receive
a reference signal from the eNB; perform measurement using the
reference signal in the measurement resource; and transmit a result
of the measurement to the eNB, wherein the measurement resource is
determined based on whether a same resource is used for DL or UL in
an adjacent eNB.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless access system,
and more particularly, a method for measuring a wireless
communication state in a wireless access system for supporting an
environment in which amounts of uplink (UL) and downlink (DL)
resources are dynamically changed, and an apparatus for supporting
the method.
BACKGROUND ART
[0002] Mobile communication systems have been developed in order to
provide voice services while ensuring the activity of users.
However, a mobile communication system have gradually extended its
field to data services as well as voice services and have been
currently developed so as to provide high speed data services.
However, in a mobile communication system that currently provides
services, resources are insufficient and users require higher speed
services, and thus, there has been a need for a more developed
mobile communication system.
[0003] One of most important factors among requirements of a
next-generation wireless access system is to support high data
transfer rate requirement. To this end, researches have been
conducted into various technologies such as multiple input multiple
output (MIMO), cooperative multiple point transmission (CoMP),
relay, etc.
[0004] A conventional wireless access system, because uplink (UL)
resources and downlink (DL) resources are fixedly configured, even
if UL and DL traffic are changed, traffic is processed within
limited resources. However, in consideration of an environment in
which an eNB dynamically changes the amounts of UL and DL resources
according to the amount of UL and DL traffic, even UL resource can
be used as DL resource, and even DL resource can be used as UL
resource. In this situation, even if resource is configured for UL
or DL, a UE needs to perform an appropriate operation according to
use of the corresponding resource.
DISCLOSURE
Technical Problem
[0005] An object of the present invention devised to solve the
problem lies in a method and apparatus for smoothly measuring a
wireless communication state by a UE in a wireless access system,
preferably, in a wireless access system for supporting an
environment in which amounts of uplink (UL) and downlink (DL)
resources are dynamically changed.
[0006] Another object of the present invention devised to solve the
problem lies in a method and apparatus for measuring a wireless
communication state in UL resource and/or DL resource by a UE in a
wireless access system, preferably, in a wireless access system for
supporting an environment in which amounts of UL and DL resources
are dynamically changed.
[0007] Another object of the present invention devised to solve the
problem lies in a method and apparatus effectively determining
resource (UL resource or DL resource) in which a UE is supposed to
communicate in a wireless access system, preferably, in a wireless
access system for supporting an environment in which amounts of UL
and DL resources are dynamically changed.
[0008] It is to be understood that both the foregoing general
description and the following detailed description of the present
invention are exemplary and explanatory and are intended to provide
further explanation of the invention as claimed.
Technical Solution
[0009] The object of the present invention can be achieved by
providing a method for supporting measurement of a user equipment
(UE) in a wireless access system for supporting an environment in
which amounts of uplink (UL) and downlink (DL) resources are
dynamically changed, the method including transmitting information
about measurement resource to the UE, transmitting a reference
signal to the UE, and receiving a result of the measurement using
the reference signal in the measurement resource, from the UE,
wherein the measurement resource is determined in consideration of
whether the same resource is used for DL or UL in an adjacent
eNB.
[0010] In another aspect of the present invention, provided herein
is an eNB for supporting measurement of a user equipment (UE) in a
wireless access system for supporting an environment in which
amounts of uplink (UL) and downlink (DL) resources are dynamically
changed, the eNB including a radio frequency (RF) unit for
transmitting and receiving a radio signal, and a processor for
information about measurement resource to the UE, transmitting a
reference signal to the UE, and receiving a result of the
measurement using the reference signal in the measurement resource,
from the UE, wherein the measurement resource is determined in
consideration of whether the same resource is used for DL or UL in
an adjacent eNB.
[0011] The measurement resource may be configured only in a
subframe used for DL transmission by the adjacent eNB.
[0012] The method may further include transmitting indication
information indicating that the measurement resource is valid when
the measurement resource is configured as UL resource.
[0013] The measurement resource may be divided into first
measurement resource and second measurement resource, the first
measurement resource may be configured only in a subframe used for
DL transmission by the adjacent eNB, and the second measurement
resource may be configured only in a subframe used for UL
transmission by the adjacent eNB.
[0014] The measurement may include at least one of reference signal
received power (RSRP) measurement, reference signal received
quality (RSRQ) measurement, received signal strength indicator
(RSSI) measurement, and radio link monitoring (RLM)
measurement.
[0015] The RSRP may be measured only in DL resource, and the RSSI
may be measured only in UL resource used for DL transmission.
[0016] In a case of the RSSI measurement, a result of the
measurement may include distribution information of measured RSSI
values measured over a plurality of predetermined subframes.
[0017] The distribution information may include at least one of
maximum and minimum of RSSI values measured over a plurality of
predetermined subframes, a frequency at which RSSI that is equal to
or more than a predetermined threshold or is equal to or less than
the predetermined threshold is measured over the plural
predetermined subframes, information of a subframe in which the
RSSI that is equal to or more than a predetermined threshold or is
equal to or less than the predetermined threshold is measured over
the plural predetermined subframes, an average value of measured
RSSI values that are equal to or more than a predetermined
threshold or equal to or less than the predetermined threshold over
the plural predetermined subframes, an measured RSSI value
corresponding to predetermined top or low percentage among measured
RSSI values measured over the plural predetermined subframes, and
an average value of measured RSSI values corresponding to
predetermined top or low percentage among measured RSSI values
measured over the plural predetermined subframes.
[0018] In another aspect of the present invention, provided herein
is a method of performing measurement in a wireless access system
for supporting an environment in which amounts of uplink (UL) and
downlink (DL) resources are dynamically changed, the method
including receiving information about measurement resource from an
eNB, receiving a reference signal from the eNB, performing
measurement using the reference signal in the measurement resource,
and transmitting a result of the measurement to the eNB, wherein
the measurement resource is determined in consideration of whether
the same resource is used for DL or UL in an adjacent eNB.
[0019] In another aspect of the present invention, provided herein
is a user equipment (UE) for performing measurement in a wireless
access system for supporting an environment in which amounts of
uplink (UL) and downlink (DL) resources are dynamically changed,
the UE including a radio frequency (RF) unit for transmitting and
receiving a radio signal, and a processor for information about
measurement resource from an eNB, receiving a reference signal from
the eNB, performing measurement using the reference signal in the
measurement resource, and transmitting a result of the measurement
to the eNB, wherein the measurement resource is determined in
consideration of whether the same resource is used for DL or UL in
an adjacent eNB.
[0020] The method may further include transmitting indication
information indicating that the measurement resource is valid when
the measurement resource is configured as UL resource.
[0021] The measurement resource may be divided into first
measurement resource and second measurement resource, the first
measurement resource is configured only in a subframe used for DL
transmission by the adjacent eNB, and the second measurement
resource is configured only in a subframe used for UL transmission
by the adjacent eNB.
[0022] The measurement may include at least one of reference signal
received power (RSRP) measurement, reference signal received
quality (RSRQ) measurement, received signal strength indicator
(RSSI) measurement, and radio link monitoring (RLM)
measurement.
[0023] The RSRP may be measured only in DL resource, and the RSSI
may be measured only in UL resource used for DL transmission.
[0024] In a case of the RSSI measurement, a result of the
measurement may include distribution information of measured RSSI
values measured over a plurality of predetermined subframes.
[0025] The distribution information may include at least one of
maximum and minimum of RSSI values measured over a plurality of
predetermined subframes, a frequency at which RSSI that is equal to
or more than a predetermined threshold or is equal to or less than
the predetermined threshold is measured over the plural
predetermined subframes, information of a subframe in which the
RSSI that is equal to or more than a predetermined threshold or is
equal to or less than the predetermined threshold is measured over
the plural predetermined subframes, an average value of measured
RSSI values that are equal to or more than a predetermined
threshold or equal to or less than the predetermined threshold over
the plural predetermined subframes, an measured RSSI value
corresponding to predetermined top or low percentage among measured
RSSI values measured over the plural predetermined subframes, and
an average value of measured RSSI values corresponding to
predetermined top or low percentage among measured RSSI values
measured over the plural predetermined subframes.
Advantageous Effects
[0026] According to embodiments of the present invention, a
wireless communication state can be smoothly measured in a wireless
access system, preferably, in a wireless access system for
supporting an environment in which amounts of uplink (UL) and
downlink (DL) resources are dynamically changed.
[0027] According to the embodiments of the present invention,
measurement can be more accurately and stably performed by
performing measurement in UL resource and/or DL resource in
consideration of a transmission direction of an adjacent cell in a
wireless access system, preferably, in a wireless access system for
supporting an environment in which amounts of UL and DL resources
are dynamically changed.
[0028] According to the embodiments of the present invention, a
corresponding user equipment (UE) can be most appropriately
scheduled in resource in which a combination of a communication
direction of a serving cell and a communication direction of an
adjacent cell is used according to a situation of each UE in a
wireless access system, preferably, in a wireless access system for
supporting an environment in which amounts of UL and DL resources
are dynamically changed.
[0029] It will be appreciated by persons skilled in the art that
that the effects that could be achieved with the present invention
are not limited to what has been particularly described hereinabove
and other advantages of the present invention will be more clearly
understood from the following detailed description taken in
conjunction with the accompanying drawings.
DESCRIPTION OF DRAWINGS
[0030] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention.
[0031] In the drawings:
[0032] FIG. 1 illustrates physical channels and a general method
for transmitting signals on physical channels in a 3rd generation
partnership project long term evolution (3GPP LTE) system;
[0033] FIG. 2 illustrates a structure of a radio frame used in a
3GPP LTE;
[0034] FIG. 3 illustrates the structure of a downlink (DL) resource
grid for the duration of one DL slot;
[0035] FIG. 4 illustrates a structure of a DL subframe;
[0036] FIG. 5 illustrates a structure of an uplink (UL)
subframe;
[0037] FIG. 6 is a schematic diagram illustrating a case in which
two adjacent cells perform transmission in different directions in
the same frequency/frequency resource;
[0038] FIG. 7 is a diagram illustrating an example of a measurement
method of a user equipment (UE) according to an embodiment of the
present invention;
[0039] FIG. 8 is a schematic diagram illustrating a case in which a
UE performs measurement for DL resource according to an embodiment
of the present invention; and
[0040] FIG. 9 is a block diagram of a wireless communication
apparatus according to an embodiment of the present invention.
BEST MODE
[0041] Reference will now be made in detail to the exemplary
embodiments of the present invention with reference to the
accompanying drawings. The detailed description, which will be
given below with reference to the accompanying drawings, is
intended to explain exemplary embodiments of the present invention,
rather than to show the only embodiments that may be implemented
according to the invention. The following detailed description
includes specific details in order to provide a thorough
understanding of the present invention. However, it will be
apparent to those skilled in the art that the present invention may
be practiced without such specific details.
[0042] In some instances, well-known structures and devices are
omitted in order to avoid obscuring the concepts of the present
invention and important functions of the structures and devices are
shown in block diagram form.
[0043] The embodiments of the present invention are disclosed on
the basis of a data communication relationship between a base
station and a terminal. In this case, the base station is used as a
terminal node of a network via which the base station can directly
communicate with the terminal. Specific operations to be conducted
by the base station in the present invention may also be conducted
by an upper node of the base station as necessary. In other words,
it will be obvious to those skilled in the art that various
operations for enabling the base station to communicate with the
terminal in a network composed of several network nodes including
the base station will be conducted by the base station or other
network nodes other than the base station. The term "base station
(BS)" may be replaced with a fixed station, Node-B, eNode-B (eNB),
or an access point (AP) as necessary. The term "relay" may be
replaced with the terms relay node (RN) or relay station (RS). The
term "terminal" may also be replaced with a user equipment (UE), a
mobile station (MS), a mobile subscriber station (MSS), a
subscriber station (SS), an advanced mobile station (AMS), a
wireless terminal (WT), a machine-type communication (MTC) device,
a machine-to-machine (M2M) device, or a device-to-device (D2D)
device as necessary.
[0044] It should be noted that specific terms disclosed in the
present invention are proposed for convenience of description and
better understanding of the present invention, and the use of these
specific terms may be changed to other formats within the technical
scope or spirit of the present invention.
[0045] Exemplary embodiments of the present invention are supported
by standard documents disclosed for at least one of wireless access
systems including an institute of electrical and electronics
engineers (IEEE) 802 system, a 3.sup.rd generation partnership
project (3GPP) system, a 3GPP long term evolution (LTE) system, an
LTE-advanced (LTE-A) system, and a 3GPP2 system. In particular,
steps or parts, which are not described to clearly reveal the
technical idea of the present invention, in the embodiments of the
present invention may be supported by the above documents. All
terminology used herein may be supported by at least one of the
above-mentioned documents.
[0046] The following embodiments of the present invention can be
applied to a variety of wireless access technologies, for example,
code division multiple access (CDMA), frequency division multiple
access (FDMA), time division multiple access (TDMA), orthogonal
frequency division multiple access (OFDMA), single carrier
frequency division multiple access (SC-FDMA), and the like. CDMA
may be embodied through wireless (or radio) technology such as
universal terrestrial radio access (utra) or CDMA2000. TDMA may be
embodied through wireless (or radio) technology such as global
system for mobile communication (GSM)/general packet radio service
(GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA may be
embodied through wireless (or radio) technology such as institute
of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE
802.16 (WiMAX), IEEE 802-20, and evolved UTRA (E-UTRA). UTRA is a
part of universal mobile telecommunications system (UMTS). 3rd
generation partnership project (3GPP) long term evolution (LTE) is
a part of E-UMTS (Evolved UMTS), which uses E-UTRA. 3GPP LTE
employs OFDMA in downlink and employs SC-FDMA in uplink.
LTE-Advanced (LTE-A) is an evolved version of 3GPP LTE.
[0047] For clarity, the following description focuses on IEEE
802.11 systems. However, technical features of the present
invention are not limited thereto.
[0048] 1. 3GPP LTE/LTE-a System to which the Present Invention is
Applicable
[0049] 1.1. Overview of System
[0050] FIG. 1 illustrates physical channels and a general method
for transmitting signals on the physical channels in the 3GPP LTE
system.
[0051] When a UE is powered on or enters a new cell, the UE
performs initial cell search (S101). The initial cell search
involves acquisition of synchronization to an eNB. Specifically,
the UE synchronizes its timing to the eNB and acquires information
such as a cell identifier (ID) by receiving a primary
synchronization channel (P-SCH) and a secondary synchronization
channel (S-SCH) from the eNB.
[0052] Then the UE may acquire information broadcast in the cell by
receiving a physical broadcast channel (PBCH) from the eNB. During
the initial cell search, the UE may monitor a DL channel state by
receiving a downlink reference signal (DL RS).
[0053] After the initial cell search, the UE may acquire more
detailed system information by receiving a physical downlink
control channel (PDCCH) and receiving a physical downlink shared
channel (PDSCH) based on information of the PDCCH (S102).
[0054] To complete access to the eNB, the UE may perform a random
access procedure with the eNB (S103 to S106). In the random access
procedure, the UE may transmit a preamble on a physical random
access channel (PRACH) (S103) and may receive a response message to
the preamble on a PDCCH and a PDSCH associated with the PDCCH
(S104). In the case of a contention-based random access, the UE may
additionally perform a contention resolution procedure including
transmission of an additional PRACH (S105) and reception of a PDCCH
signal and a PDSCH signal corresponding to the PDCCH signal (S
106).
[0055] After the above procedure, the UE may receive a PDCCH and/or
a PDSCH from the eNB (S107) and transmit a Physical Uplink Shared
Channel (PUSCH) and/or a Physical Uplink Control Channel (PUCCH) to
the eNB (S108), in a general UL/DL signal transmission
procedure.
[0056] Control information that the UE transmits to the eNB is
called uplink control information (UCI). The UCI includes hybrid
automatic repeat and request acknowledgement/negative
acknowledgement (HARQ-ACK/NACK), scheduling request (SR), channel
quality indication (CQI), precoding matrix index (PMI), a rank
indication (RI), etc.
[0057] In the LTE system, UCI is generally transmitted on a PUCCH
periodically. However, if control information and traffic data
should be transmitted simultaneously, they may be transmitted on a
PUSCH. In addition, UCI may be transmitted periodically on the
PUSCH, upon receipt of a request/command from a network.
[0058] FIG. 2 illustrates a structure of a radio frame used in a
3GPP LTE.
[0059] In a cellular orthogonal frequency division multiplexing
(OFDM) wireless packet communication system, UL/DL data packets are
transmitted in subframes. One subframe is defined as a
predetermined time interval including a plurality of OFDM symbols.
The 3GPP LTE standard supports a type 1 radio frame structure
applicable to frequency division duplex (FDD) and a type 2 radio
frame structure applicable to time division duplex (TDD).
[0060] FIG. 2(a) is a diagram illustrating the structure of the
type 1 radio frame. A DL radio frame includes 10 subframes, each
subframe including two slots in the time domain. A time required
for transmitting one subframe is defined as a transmission time
interval (TTI). For example, one subframe may be 1 ms long and one
slot may be 0.5 ms long. One slot includes a plurality of OFDM
symbols in the time domain and a plurality of resource blocks (RBs)
in the frequency domain. Since the 3GPP LTE system uses OFDMA for
DL, an OFDM symbol may be one symbol period. The OFDM symbol may be
called an SC-FDMA symbol or symbol period. An RB is a resource
allocation unit including a plurality of contiguous subcarriers in
one slot.
[0061] The number of OFDM symbols included in one slot may be
changed according to the configuration of a cyclic prefix (CP).
There are two types of CPs, extended CP and normal CP. For example,
if each OFDM symbol is configured to include a normal CP, one slot
may include 7 OFDM symbols. If each OFDM symbol is configured to
include an extended CP, the length of an OFDM symbol is increased
and thus the number of OFDM symbols included in one slot is less
than that in the case of a normal CP. In the case of the extended
CP, for example, one slot may include 6 OFDM symbols. If a channel
state is instable as is the case with a fast UE, the extended CP
may be used in order to further reduce inter-symbol
interference.
[0062] In the case of the normal CP, since one slot includes 7 OFDM
symbols, one subframe includes 14 OFDM symbols. Up to first three
OFDM symbols of each subframe may be allocated to a PDCCH and the
remaining OFDM symbols may be allocated to a PDSCH.
[0063] FIG. 2(b) illustrates the structure of the type 2 radio
frame. The type 2 radio frame includes two half frames, each half
frame including 5 subframes, a downlink pilot time slot (DwPTS), a
guard period (GP), and an uplink pilot time slot (UpPTS). One
subframe is divided into two slots. The DwPTS is used for initial
cell search, synchronization, or channel estimation at a UE, and
the UpPTS is used for channel estimation and UL transmission
synchronization with a UE at an eNB. The GP is used to cancel UL
interference between UL and DL, caused by the multi-path delay of a
DL signal.
[0064] UL-DL configuration of the type 2 radio frame structure of a
TDD system refers to a rule indicating whether UL and DL are
allocated (or reserved) to all subframes. Table 1 shows an
exemplary uplink-downlink configuration.
TABLE-US-00001 TABLE 1 Uplink- Downlink- downlink to-Uplink config-
Switch-point Subframe number uration periodicity 0 1 2 3 4 5 6 7 8
9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S
U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U D D D D
D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U D
[0065] In Table 3 above, for each respective subframe of a radio
frame, "D" denotes a downlink subframe, "U" denotes an uplink
subframe, and "S" denotes a special subframe including three fields
of a DwPTS, a GP, and a an UpPTS. The UL-DL configuration may be
classified into 7 types, and for each respective configurations,
the locations and numbers of DL subframes, special subframes, and
UL subframes are varied.
[0066] A point in time for converting DL into UL or a pint in time
for converting UL into DL is referred to as a switching point. A
switch-point periodicity refers to a period with which an operation
of conversion between a UL subframe and a DL subframe is repeated
and supports both 5 ms and 10 ms. In the case of DL-UL switch-point
periodicity of 5 ms, a special subframe S is present every
half-frame. In the case of DL-UL switch-point periodicity of 5 ms,
a special subframe S is present only in a first half-frame.
[0067] In all configurations, subframes #0 and #5 and a DwPTS are
period for DL transmission only. The UpPTS, a subframe, and a
subframe immediately subsequent thereto are always periods for UL
transmission.
[0068] The UL-DL configuration may be system information and may be
known to both an eNB and a UE. Whenever UL-DL configuration
information is changed, the eNB may transmit only an index of
configuration information to notify the UE of information about
change in UL-DL allocation state of a radio frame. In addition, the
configuration information may be transmitted as a type of DL
control information through a physical downlink control channel
(PDCCH) and may be commonly transmitted as a type of broadcast
information to all UEs in a cell through a broadcast channel like
other scheduling information and
[0069] The aforementioned radio frame structure is purely
exemplary. The number of subframes included in a radio frame or the
number of slots included in each subframe, and the number of
symbols of each slot can be changed in various ways.
[0070] FIG. 3 illustrates the structure of a DL resource grid for
the duration of one DL slot. Referring to FIG. 3, one DL slot
includes a plurality of OFDM symbols in the time domain Here, one
DL slot includes 7 OFDM symbols and one resource block includes 12
subcarriers in the frequency symbol, which is purely exemplary, but
embodiments of the present invention are not limited thereto.
[0071] Each element of the resource grid is referred to as a
resource element (RE). An RB includes 12.times.7 REs. The number of
RBs in a DL slot, N.sup.DL depends on a DL transmission bandwidth.
A UL slot may have the same structure as a DL slot.
[0072] FIG. 4 illustrates a structure of a DL subframe.
[0073] Referring to FIG. 4, up to three or four OFDM symbols at the
start of the first slot of a DL subframe are used as a control
region to which control channels are allocated and the other OFDM
symbols of the DL subframe are used as a data region to which a
PDSCH is allocated. DL control channels defined for the 3GPP LTE
system include a physical control format indicator channel
(PCFICH), a physical downlink control channel (PDCCH), and a
physical hybrid-ARQ indicator channel (PHICH).
[0074] The PCFICH is located in the first OFDM symbol of a
subframe, carrying information about the number of OFDM symbols
used for transmission of control channels in the subframe. The
PHICH delivers an HARQ ACK/NACK signal as a response to a UL
transmission. Control information carried on the PDCCH is called
downlink control information (DCI). The DCI transports resource
allocation information and other control information for a UE or a
UE group. For example, the DCI includes DL/UL scheduling
information, UL transmission (Tx) power control commands, etc.
[0075] The PDCCH delivers information about resource allocation and
a transport format for a downlink shared channel (DL-SCH),
information about resource allocation and a transport format for an
uplink shared channel (UL-SCH), paging information of a paging
channel (PCH), system information on the DL-SCH, information about
resource allocation for a higher-layer control message such as a
random access response transmitted on the PDSCH, a set of Tx power
control commands for individual UEs of a UE group, Tx power control
commands, voice over Internet protocol (VoIP) activation indication
information, etc. A plurality of PDCCHs may be transmitted in the
control region. A UE may monitor a plurality of PDCCHs. A PDCCH is
transmitted in an aggregate of one or more consecutive Control
Channel Elements (CCEs). A CCE is a logical allocation unit used to
provide a PDCCH at a coding rate based on the state of a radio
channel. A CCE includes a plurality of RE groups (REGs). The format
of a PDCCH and the number of available bits for the PDCCH are
determined according to the number of CCEs and a coding rate
provided by the CCEs.
[0076] An eNB determines a PDCCH format according to DCI
transmitted to a UE and adds a cyclic redundancy check (CRC) to
control information. The CRC is masked by an identifier (ID) known
as a radio network temporary identifier (RNTI) according to the
owner or usage of the PDCCH. If the PDCCH is destined for a
specific UE, the CRC may be masked by a cell-RNTI (C-RNTI) of the
UE. If the PDCCH carries a paging message, the CRC of the PDCCH may
be masked by a paging indicator identifier (P-RNTI). If the PDCCH
carries system information, particularly, a system information
block (SIB), its CRC may be masked by a system information ID and a
system information RNTI (SI-RNTI). To indicate that the PDCCH
carries a random access response to a random access preamble
transmitted by a UE, its CRC may be masked by a random access-RNTI
(RA-RNTI).
[0077] FIG. 5 illustrates a structure of a UL subframe.
[0078] Referring to FIG. 5, a UL subframe may be divided into a
control region and a data region in the frequency domain. The
control region includes a PUCCH that carriers UL control
information. The data region includes a PUSCH that carrier user
data. In order to maintain single carrier wave properties, one UE
may not simultaneously transmit a PUCCH and a PUSCH. An RB pair is
allocated to a PUCCH of one UE in a subframe. RBs included in an RB
pair occupy different subcarriers in two respective slots. The RB
pair allocated to the PUCCH frequency-hops over a slot
boundary.
[0079] 1.2. DL Measurement
[0080] In a mobile communication system, a packet (or signal) is
transmitted on a radio channel from a transmitter to a receiver. In
view of the nature of the radio channel, the packet may be
distorted during the transmission. To receive the signal
successfully, the receiver should compensate for the distortion in
the received signal using channel information. Generally, to enable
the receiver to acquire the channel information, the transmitter
transmits a signal known to both the transmitter and the receiver
and the receiver acquires knowledge of channel information based on
the distortion of the signal received on the radio channel. The
signal known to both the transmitter and receiver is referred to as
a pilot signal or a reference signal (RS).
[0081] In transmission and reception of data using multiple
antennas, the receiver needs to know channel states between
transmit antennas and receive antennas to successfully receive a
signal. Accordingly, a separate reference signal is needed for each
transmit antenna.
[0082] In a wireless communication system, an RS can be largely
classified into two types according to its purpose. The RS includes
an RS for channel information acquisition and an RS for data
demodulation. The former is used for acquisition of channel
information to DL by a UE. Thus the former RS needs to be
transmitted in a wideband, and even a UE that does not receive DL
data in a specific subframe needs to receive and measure the RS. In
addition, the RS for channel measurement may also be used for
measurement of handover, etc. The latter is an RS that is
transmitted together with corresponding resource when an eNB
transmits a DL signal. In this regard, the UE can receive the
corresponding RS to estimate a channel and accordingly demodulate
data. The RS for data demodulation needs to be transmitted in a
region in which data is transmitted.
[0083] A 3GPP LTE system defines a common reference signal (CRS)
shared by all UEs in a cell and a dedicated reference signal (DRS)
for a specific UE only as a DL RS. The CRS may be used for both
channel information acquisition and data demodulation and may also
be referred to as a cell-specific RS. An eNB transmits the CRS
every subframe over a wideband. On the other hand, the DRS may be
used for data demodulation only and may be transmitted through REs
when data modulation on a PDSCH is required. The UE may receive
whether the DRS is present through a higher layer and determines
that the DRS is valid only when the corresponding PDSCH is mapped.
The DRS may be referred to as a UE-specific RS or a demodulation RS
(DMRS).
[0084] A receiver (UE) may estimate a channel state from the CRS
and feedback an indicator associated with channel quality, such as
a channel quality indicator (CQI), a precoding matrix index (PMI),
and/or a rank indicator (RI) to a transmitter (eNB). In addition,
the receiver may define an RS associated with feedback of channel
state information (CSI) such as CQI/PMI/RI as a separate CSI-RS. A
CSI-RS for channel measurement is designed mainly for channel
measurement unlike an existing CRS used for data demodulation as
well as channel measurement, etc. Since the CSI-RS is transmitted
only for transmission of information about a channel state, the eNB
transmits CSI-RSs about all antenna ports. In addition, the CSI-RS
is transmitted for knowledge of DL channel information and thus is
transmitted over all bands unlike a DRS.
[0085] A current 3GPP LTE system defines two types of a closed-loop
MIMO transmission scheme and an open-loop MIMO scheme managed
without channel information of the receiver. In the closed-loop
MIMO, in order to achieve multiplexing gain of a MIMO antenna, each
of the transmitter and the receiver performs beamforming based on
channel information, that is, channel state information (CSI). The
eNB may command the UE to allocate a physical uplink control
channel (PUCCH) or a physical uplink shared channel (PUSCH) and to
feedback DL CSI in order to acquire CSI from the UE.
[0086] CSI is classified largely into three information types, a
rank indicator (RI), a precoding matrix index (PMI), and a channel
quality indication (CQI).
[0087] An RI is information about a channel rank that is the number
of signal streams (or layers) that a UE can receive in the same
time-frequency resources. Because the RI is determined dominantly
according to the long-term fading of a channel, the RI may be fed
back to an eNB in a longer period than a PMI and a CQI.
[0088] A PMI is the index of a UE-preferred eNB precoding matrix
determined based on a metric such as signal to interference and
noise ratio (SINR), reflecting the spatial characteristics of
channels. The PMI reflects channel spatial characteristics and
indicates a precoding index of an eNB preferred by a UE based on a
metric such as a signal to interference plus noise ratio (SINR),
etc. That is, the PMI is information about a precoding matrix used
for transmitted from a transmitter. The precoding matrix fed back
from a received is determined in consideration of the number of a
layer indicted by an RI. The PMI may be fed back in case of
closed-loop spatial multiplexing (SM) and large delay cyclic delay
diversity (CDD). In the case of open-loop transmission, the
transmitter may select a precoding matrix according to
predetermined rules. A process for selecting a PMI for each rank is
as follows. The receiver may calculate a post processing SINR in
each PMI, convert the calculated SINR into the sum capacity, and
select the best PMI on the basis of the sum capacity. That is, PMI
calculation of the receiver may be considered to be a process for
searching for an optimum PMI on the basis of the sum capacity. The
transmitter that has received PMI feedback from the receiver may
use a precoding matrix recommended by the receiver. This fact may
be contained as a 1-bit indicator in scheduling allocation
information for data transmission to the receiver. Alternatively,
the transmitter may not use the precoding matrix indicated by a PMI
fed back from the transmitter. In this case, precoding matrix
information used for data transmission from the transmitter to the
receiver may be explicitly contained in the scheduling allocation
information.
[0089] A CQI represents a channel strength and in general reflects
a reception SINR that the eNB can achieve with a PMI. A UE reports
CQI index to an eNB. The CQI index indicates a specific combination
of a set including combination of a predetermined modulation scheme
and code rate.
[0090] In an evolved communication system such as LTE-A, additional
multi-user diversity gain is obtained using multi-user MIMO
(MU-MIMO). The MU-MIMO technology refers to a method of a scheme in
which an eNB assigns antenna resources to different UEs and selects
and schedules a UE that can have a high data transfer rate for each
antenna. For the multi-user diversity gain, higher accuracy is
required from a viewpoint of a channel feedback. Since interference
is present between UEs multiplexed in the antenna domain in
MU-MIMO, accuracy of CSI may largely affect not only a UE that
reports the CSI but also interference of other multiplexed UEs.
Accordingly, in order to enhance the accuracy of a feedback channel
in LTE-A system, a final PMI may be determined to be divided into
W1 corresponding to a long-term and/or wideband PMI and W2
corresponding to a short-term and/or subband PMI and may be
determined as a combination of W1 and W2.
[0091] For example, the long-term covariance matrix of channels
expressed as [Equation 1] may be used for hierarchical codebook
transformation that configures one final PMI with W1 and W2 from
information of two channels.
W=norm(W1W2) [Equation 1]
[0092] In [Equation 1], W2 is a short-term PMI, which is a codeword
of a codebook reflecting short-term channel information, W1 is a
long-term covariance matrix, and norm(A) is a matrix obtained by
normalizing the norm of each column of matrix A to 1. W is a
codeword of a final transformed codebook. Conventionally, W1 and W2
are given according to [Equation 2] below.
W 1 ( i ) = [ X i 0 0 X i ] , where X i is Nt / 2 by M matrix W 2 (
j ) = [ e M k .alpha. j e M k e M l .beta. j e M l e M m .gamma. j
e M m ] r columns ( if rank = r ) , where 1 .ltoreq. k , l , m
.ltoreq. M and k , l , m are integer . [ Equation 2 ]
##EQU00001##
[0093] In [Equation 2] above, the codewords are designed so as to
reflect correlation characteristics between established channels,
if cross polarized antennas are arranged densely (for example, the
distance between adjacent antennas is equal to or less than a half
of a signal wavelength. The cross polarized antennas may be divided
into a horizontal antenna group and a vertical antenna group and
the two antenna groups are co-located, each having the property of
a uniform linear array (ULA) antenna. Therefore, the correlations
between antennas in each group have the same linear phase increment
property and the correlation between the antenna groups is
characterized by phase rotation. Since a codebook is eventually
quantized values of channels, it is necessary to design a codebook,
reflecting channel characteristics. For the convenience of
description, a rank-1 codeword designed according to [Equation 2]
may be given as [Equation 3] below.
W 1 ( i ) * W 2 ( j ) = [ X i ( k ) .alpha. j X i ( k ) ] [
Equation 3 ] ##EQU00002##
[0094] In [Equation 3] above, a codeword is expressed as an
N.sub.T.times.1 vector where NT is the number of Tx antennas and
the codeword is composed of an upper vector X.sub.i(k) and a lower
vector .alpha..sub.iX.sub.i(k), representing the correlation
characteristics of the horizontal and vertical antenna groups,
respectively. Preferably, X.sub.i(k) is expressed as a vector
having the linear phase increment property, reflecting the
correlation characteristics between antennas in each antenna group.
For example, a discrete Fourier transform (DFT) matrix may be used
for X.sub.i(k).
[0095] Higher accuracy is required for CoMP. In the case of CoMP
JT, a plurality of eNBs collaboratively transmits the same data to
a specific UE, and thus, a CoMP JT system may be academically
considered as a MIMO system in which antennas are geographically
distributed. That is, when the JT performs MU-MIMO, high level
channel accuracy is also required in order to prevent co-scheduled
UEs like single cell MU-MIMO. In the case of CoMP CB, accurate
channel information is also required in order to prevent
interference to a serving cell by an adjacent cell.
[0096] Recently, active research has been conducted into enhanced
inter-cell interference coordination (eICIC) as an interference
coordination method between UEs in a 3GPP LTE-A system. The eICIC
is one of interference coordination methods. In this regard,
according to the eICIC, a cell causing interference is defined as
an aggressor cell or a primary cell, an interfered cell is defined
as a victim cell or a secondary cell, the aggressor cell stops data
transmission in some specific resource regions such that a UE can
maintain access to the victim cell or secondary cell in the
corresponding resource region. That is, time domain inter-cell
interference coordination by which an aggressor cell uses a silent
subframe that reduces transmission power/activity of some physical
channels (including operation of setting zero power) and a victim
cell schedules UEs in consideration of the silent frame can be
used. The silent subframe may also be called an almost blank
subframe (ABS). In this case, from a viewpoint of a UE positioned
in the victim cell, an interference level largely changes according
to whether the silent subframe is present, and signals transmitted
from the aggressor cell and the victim cell may act as interference
to a UE positioned at a boundary between the aggressor cell and the
victim cell.
[0097] In this situation, to perform more accurate radio link
monitoring (RLM) in each subframe or radio resource management
(RRM) for measuring reference signal received power
(RSRP)/reference signal received quality (RSRQ) or to measure
channel state information (CSI) for link adaptation, the
aforementioned monitoring/measurement needs to be limited to
subframe sets having uniform interference characteristics.
[0098] In 3GPP LTE system, the following restricted RLM and RRM/CSI
measurement is defined.
[0099] 1) RLM
[0100] The DL radio link quality may be monitored by a physical
layer of a UE in order to indicate an `out-of-sync` or `in-sync`
status to higher layers.
[0101] In the case of a non-discontinuous reception (DRX) mode
operation, the physical layer in the UE compares a value measured
over a previous time period every radio frame with thresholds
(Q.sub.out and Q.sub.in) to monitor radio link quality. On the
other hand, in the case of a DRX mode operation, the physical layer
in the UE compares a value measured over a previous time period
every DRX period at least once to monitor radio link quality. Here,
if higher layer signaling indicates specific subframes for
restricted radio link monitoring, the radio link quality is not
monitored by other subframes other than the indicated
subframes.
[0102] The physical layer in the UE indicates `out-of-sync` to
higher layers when the radio link quality is worse than the
threshold Q.sub.out in radio frames in which the radio link quality
is assessed. That is, the `out-of-sync` indication is an event that
occurs when a UE measures the channel quality of a signal from a
serving eNB and the channel quality is degraded to a predetermined
level or less. Here, the channel quality may be measured from a
signal-to-noise ratio (SNR) measured using a cell-specific
reference signal (CRS) of a DL signal from the eNB. In addition,
the `out-of-sync` indication may be provided to higher layers when
a PDCCH received from lower layers (physical layers) cannot be
demodulated or signal-to-interference plus noise ratio (SINR) is
low.
[0103] On the other hand, when the physical layer in the UE is
better than the threshold Q.sub.in in radio frames in which the
radio link quality is assessed, `in-sync` is indicated to higher
layers. That is, the `in-sync` indication is an event that occurs
when a UE measures the channel quality of a signal from a serving
eNB and the channel quality is increased to a predetermined level
or more.
[0104] 2) Channel Quality Indicator (CQI)
[0105] CQI is information regarding channel quality. CQI may be
represented by a predetermined MCS combination. CQI index may be
given as shown in Table 2 below.
[0106] Table 2 shows CQI index.
TABLE-US-00002 TABLE 2 CQI index modulation code rate x 1024
efficiency 0 out of range 1 QPSK 78 0.1523 2 QPSK 120 0.2344 3 QPSK
193 0.3770 4 QPSK 308 0.6016 5 QPSK 449 0.8770 6 QPSK 602 1.1758 7
16QAM 378 1.4766 8 16QAM 490 1.9141 9 16QAM 616 2.4063 10 64QAM 466
2.7305 11 64QAM 567 3.3223 12 64QAM 666 3.9023 13 64QAM 772 4.5234
14 64QAM 873 5.1152 15 64QAM 948 5.5547
[0107] Table 3 below shows a PDSCH transmission scheme for CSI
reference resource.
TABLE-US-00003 TABLE 3 Transmission mode Transmission scheme of
PDSCH 1 Single-antenna port, port 0 2 Transmit diversity 3 Transmit
diversity if the associated rank indicator is 1, otherwise large
delay CDD 4 Closed-loop spatial multiplexing 5 Multi-user MIMO 6
Closed-loop spatial multiplexing with a single transmission layer 7
If the number of PBCH antenna ports is one, Single-antenna port,
port 0; otherwise Transmit diversity 8 If the UE is configured
without PMI/RI reporting: if the number of PBCH antenna ports is
one, single-antenna port, port 0; otherwise transmit diversity If
the UE is configured with PMI/RI reporting: closed-loop spatial
multiplexing 9 If the UE is configured without PMI/RI reporting: if
the number of PBCH antenna ports is one, single-antenna port, port
0; otherwise transmit diversity Closed-loop spatial multiplexing
with up to 8 layer transmission, ports 7-14 (see subclause
7.1.5B)
[0108] Referring to Table 2 above, CQI index may be represented by
4 bits (i.e., CQI indexes of 0-15). Each CQI index may indicate a
modulation scheme and a code rate.
[0109] A 3GPP LTE/LTE-A system defines that the following
assumptions are considered in order to calculate CQI index by a UE
from CSI reference resource.
[0110] (1) The first three OFDM symbols in one subframe are
occupied by control signaling.
[0111] (2) Resource elements (REs) used by a primary
synchronization signal, a secondary synchronization signal or a
physical broadcast channel (PBCH) are not present.
[0112] (3) CP length of a non-MBSFN subframe is assumed.
[0113] (4) Redundancy version is set to zero (0).
[0114] (5) In the case of CSI reporting in transmission mode 9,
when a UE configures PMI/RI reporting, DMRS overhead is the same as
most recently reported rank.
[0115] (6) REs used for CSI-RS and zero-power CSI-RS are not
present.
[0116] (7) REs used for Positioning Reference Signal (PRS) are not
present.
[0117] (8) PDSCH transmission method may be dependent upon a
current transmission mode (e.g., a default mode) configured in a
LTE and given according to Table 3 above.
[0118] (9) The ratio of PDSCH EPRE (energy per resource element) to
a cell-specific reference signal EPRE may be given with the
exception of .rho..sub.A. (A detailed description of .rho..sub.A
may follow the following assumption. Provided that a UE for an
arbitrary modulation scheme may be set to transmission mode 2
having four cell-specific antenna ports or may be set to
transmission mode 3 having an RI of 1 and four cell-specific
antenna ports, .rho..sub.A may be denoted by
.rho..sub.A=P.sub.A+.DELTA..sub.offset+10 log.sub.10(2)[dB]. In the
remaining cases, in association with an arbitrary modulation method
and the number of arbitrary layers, .rho..sub.A may be denoted by
.rho..sub.A=P.sub.A+.DELTA..sub.offset[dB]. .DELTA..sub.offset is
given by a nomPDSCH-RS-EPRE-Offset parameter configured by higher
layer signaling.)
[0119] Definition of the above-mentioned assumptions may indicate
that CQI includes not only information regarding channel quality
but also various information of a corresponding UE. That is,
different CQI indexes may be fed back according to a throughput or
performance of the corresponding UE at the same channel quality, so
that it is necessary to define a predetermined reference for the
above-mentioned assumption.
[0120] Conventional RLM/RRM measurement on a serving cell is
performed using a CRS. However, since precoding is applied in a
transmission mode (e.g., transmission mode 9) using a DMRS, the
RLM/RRM measurement may be different from measurement on link in
which actual transmission is performed. Accordingly, when a PMI/RI
reporting mode is configured in transmission mode 9, the UE
performs channel measurement in order to calculate a CQI value
based on a CSI reference signal only. On the other hand, when the
PMI/RI reporting mode is not configured in transmission mode 9, the
UE performs channel measurement for CQI calculation based on the
CRS.
[0121] A procedure in which the UE recognizes a channel state to
obtain a proper MCS may be designed in various ways for embodiment
of the UE. For example, the UE may calculate a channel state or
valid signal-to-interference plus noise ratio (SINR) using a
reference signal. In addition, the channel state or the valid SINR
can be measured on an entire system bandwidth (which is referred to
as set S) or on a partial bandwidth (specific subband or specific
RB). CQI of the entire system bandwidth (set S) may be referred to
as a wideband (WB) CQI and CQI of the partial bandwidth may be
referred to as a subband (SB) CQI. The UE may obtain the highest
MCS based on the calculated channel state or valid SINR. The
highest MCS refers to MCS satisfying the assumption of the CQI
calculation in which a decoding transfer block error rate does not
exceed 10%. The UE may determine a CQI index associated with the
calculated MCS and report the determined CQI index to the eNB.
[0122] In an LTE/LTE-A system, CSI reference resource for CSI
feedback/report is defined. The CSI reference resource is defined
as a group of DL physical resource blocks (PRBs) corresponding to a
frequency band associated with the calculated CQI in the frequency
domain. In addition, the CSI reference resource is defined as a
single DL subframe n-n.sub.CQI.sub.--.sub.ref in the time domain.
Here, n is a UL subframe index for CSI transmission/report.
[0123] In the case of periodic CSI reporting,
n.sub.CQI.sub.--.sub.ref has a smallest value corresponding to a
valid DL subframe among values equal to or more than 4. That is,
n.sub.CQI.sub.--.sub.ref corresponds to a valid DL subframe that is
most close to a UL subframe for CSI reporting among at least
4.sup.th previous subframes in a UL subframe for CSI reporting. In
addition, in the case of aperiodic CSI reporting, the CSI reference
resource may be the same as a valid DL subframe in which
corresponding CSI request in UL DCI format (e.g., DCI format 0) is
transmitted. In addition, in the aperiodic CSI reporting, when the
corresponding CSI request is transmitted in random access response
grant in the DL subframe n-n.sub.CQI.sub.--.sub.ref,
n.sub.CQI.sub.--.sub.ref is 4.
[0124] In addition, when CSI subframe sets (C.sub.CSI,0,
C.sub.CSI,1) are configured for a corresponding UE by a higher
layer, each CSI reference resource may be included in any one of
two subframe sets (C.sub.CSI,0, C.sub.CSI,1) but cannot be included
in the both subframes.
[0125] A DL subframe can be valid if i) it is configured as a DL
subframe for a corresponding UE, ii) it is not a
multicast-broadcast single frequency network (MBSFN) subframe
except for transmission mode 9, iii) it does not contain a DwPTS
field when a length of the DwPTS in a special subframe of a TDD
system is equal to or less than a predetermined length, iv) it is
not contained in a measurement gap configured for the corresponding
UE, and vi) it is an element of the CSI subframe set associated
with the periodic CSI report when the UE is configured with CSI
subframes sets for periodic CSI reporting. On the other hand, if
there is not valid DL subframe for the CSI reference resource, CSI
reporting is omitted in UL subframe n.
[0126] 3) Radio Resource Management (RRM)
[0127] Measurement for RRM may be largely classified into reference
signal received power (RSRP), reference signal received quality
(RSRQ), etc., and the RSRQ may be measured via a combination of
RSRP and E-UTRA carrier received signal strength indicator
(RSSI).
[0128] The RSRP is defined as a linear average of power
distribution of resource elements in which a cell-specific
reference signal (CRS) is transmitted in a measurement frequency
band. For RSRP determination, a cell-specific reference signal (R0)
corresponding to antenna port `0` may be used. For RSRP
determination, a cell-specific reference signal (R1) corresponding
to antenna port `1` may be further used. When reception diversity
is used by the UE, the reported value may not be smaller than the
corresponding RSRP of individual diversity branch. For RSRP
determination, a measurement frequency band used by the UE and the
number of resource elements used in a measurement period may be
determined by the UE as long as corresponding accuracy requirements
are satisfied. In addition, power per resource element may be
determined from energy from a portion of a symbol except for a
cyclic prefix (CP).
[0129] Reference signal received quality (RSRQ) is defined as
N.times.RSRP/E-UTRA carrier received signal strength indicator
(RSSI). Here, N is the number of resource blocks (REs) of an E-UTRA
carrier RSSI measurement band. In addition, in the aforementioned
formula, measurement of the numerator and the denominator may be
achieved from a set of the same RB set.
[0130] The E-UTRA carrier RSSI includes a linear average of total
reception power detected from all sources including a serving cell
and non-serving cell of a co-channel, adjacent channel
interference, thermal noise, etc. in OFDM symbols containing a
reference symbol corresponding to antenna port `0` over N resource
blocks in a measurement band. On the other hand, when specific
subframes for performing RSRQ measurement are indicated via higher
layer signaling, the RSSI is measured via all OFDM symbols in the
indicated subframes. When reception diversity is used by the UE,
the reported value may not be smaller than the corresponding RSRP
of individual diversity branch.
[0131] 2. Method of Measuring Communication State
[0132] The present invention proposes a method of measuring and
reporting a communication state in each resource by a UE in order
to notify a network of information about resource (UL resource or
DL resource) in which the UE is supposed to communicate in an
environment in which an eNB dynamically changes the amounts of UL
and DL resources according to the volume of UL and DL traffic.
[0133] FIG. 6 is a schematic diagram illustrating a case in which
two adjacent cells perform transmission in different directions in
the same frequency/frequency resource.
[0134] Referring to FIG. 6, in the same time/frequency resource of
the two adjacent cells, an eNB 1 and a UE 1 perform DL
transmission, whereas an eNB 2 in an adjacent cell and a UE 2
perform UL transmission. Likewise, when the two adjacent cells
perform transmission in different directions in the same
frequency/frequency resource, interference between cells increases
compared with a case in which two cells perform transmission in the
same direction (UL or DL), and a UE (e.g., a UE, etc. positioned at
an boundary between cells) positioned at a specific location may be
strongly interfered from the adjacent cell, and thus communication
between the adjacent cells in different directions may be
impossible. Accordingly, a UE may measure a communication state in
UL resource and/or DL resource and report the communication stat to
a network. In this case, it is very important to determine a
combination (a combination of a communication direction of a
serving cell that a UE attaches and a communication direction of an
adjacent cell) of communication directions that are most
appropriately for a situation of each UE and to schedule the
corresponding UE in time/frequency resources corresponding to the
combination.
[0135] Hereinafter, the present invention assumes a situation in
which an eNB dynamically changes the amounts of UL/DL resources
according to the volume of traffic. In order to achieve this
dynamic change, the eNB may temporarily schedule UL transmission
when UL traffic is high in resource configured as DL resource or
temporarily schedule DL transmission toward the UE using resource
configure as UL resource when DL traffic is high. Here, resource
configured as UL resource refers to a UL band in an FDD system and
refers to a UL subframe in a TDD system. On the other hand,
resource configured as DL resource refers to a DL band in an FDD
system and refers to a DL subframe in a TDD. For example, when an
eNB notifies a plurality of un-specific UEs of information
indicating that a specific subframe is configured as a UL subframe,
if the volume of DL traffic is high, the eNB may temporarily notify
a specific UE of information indicating that the corresponding
subframe is converted to be used for DL transmission. In addition,
a network may specify and separately configure resource, use of
which is dynamically changed to UL/DL resources, and in this case
it is obvious to also apply the principle of the present invention
to this case.
[0136] Hereinafter, for clarity, it is assumed that DL resource (or
a DL subframe) does not include UL resource (or a UL subframe), use
of which is temporarily changed to DL transmission, and oppositely
UL resource (or a UL subframe) does not include DL resource (or a
DL subframe), use of which is temporarily changed to UL
transmission.
[0137] According to the present invention, measurement includes RRM
measurement such as RSRP, RSRQ, and RSSI defined in a 3GPP LTE
system, or radio link monitoring (RLM) measurement for monitoring a
current basic communication state with a serving cell. Hereinafter,
for clarify, it is assumed that boundaries of UL/DL subframes
between adjacent cells are aligned.
[0138] FIG. 7 is a diagram illustrating an example of a measurement
method of a UE according to an embodiment of the present
invention.
[0139] Referring to FIG. 7, when uses of UL resource and DL
resource are dynamically changed, an eNB may transmit resource
information configured for measurement of the UE to the UE (S701).
Here, information about measurement information may be transmitted
through a higher layer signal such as an RRC layer, a MAC layer
signal, or a physical layer signal.
[0140] Since UL resource and DL resource are dynamically changed,
the UE may perform measurement for DL resource and/or UL resource
(in particular, UL resource used for DL) and the eNB may transmit
the resource information for measurement of the UE for each
respective resource. Here, the measurement resource may be
determined in consideration of whether the same resource is used
for DL or UL in an adjacent eNB. In detail, the eNB may limit
resource for performing measurement for DL resource and/or UL
resource by the UE to specific resource in consideration of whether
the same resource is used for DL or UL in an adjacent eNB in order
to receive stable report about measurement from the UE. In
addition, the eNB may configure the UE to divide sets of resources
for measurement of the UE and measure each set in consideration of
whether the same resource is used for DL or UL in an adjacent eNB
for each respective resource. In addition, the eNB may differently
configure the measurement resource for each respective measurement
metric. Resource for measurement of the UE may be pre-configured
and known to the eNB and the UE. In this case, step S701 may be
omitted.
[0141] The eNB transmits a reference signal to the UE in resource
for measurement of the UE (S705). When the UE performs measurement
for DL resource, the eNb may transmit a reference signal defined in
a legacy system to the UE in the same way, and when the UE performs
measurement for UL resource used for DL, the eNb may transmit a
reference signal configured for measurement of the UE in the
corresponding resource.
[0142] The UE may perform measurement for the corresponding
resource configured as the measurement resource (S705) and
periodically or aperiodically report the measurement result to the
eNB (S707). Here, the measurement result may include a measured
value measured by the UE in one or more subframes.
[0143] Hereinafter, a method for measuring a communication state
according to the present invention will be described in detail.
[0144] 2.1. Measurement
[0145] Hereinafter, for convenience of description, a communication
state measurement method that is divided into measurement for UL
resource and measurement for DL resource will be described with
regard to the present invention. However, needless to say,
measurement for UL resource and measurement for DL resource can be
simultaneously performed by the same UE. In addition, described
methods can be independently used but at least one or more methods
can be combined and used.
[0146] 2.1.1. Measurement for DL Resource
[0147] A UE may perform measurement for DL resource and in this
case, follow a measurement definition defined in a legacy wireless
access system (e.g., a 3GPP LTE system). This is because all
measurements are defined for DL resource in a legacy system. For
example, a CRS, a CSI-RS, or the like may be used as a reference
signal for measurement for DL resource.
[0148] However, when the UE performs measurement for DL resource,
inter-cell interferences may be much different according to whether
the same time/frequency resource as resource in which measurement
is performed is used for UL transmission or DL transmission in an
adjacent cell.
[0149] FIG. 8 is a schematic diagram illustrating a case in which a
UE performs measurement for DL resource according to an embodiment
of the present invention.
[0150] FIG. 8(a) illustrates a case in which, when a UE 1
positioned within coverage of an eNB 1 performs measurement for DL
resource, an eNB 2 of an adjacent cell performs DL transmission on
a UE 2 in resource in which the UE 1 performs measurement. FIG.
8(b) illustrates a case in which, when the UE 1 positioned within
coverage of the eNB 1 performs measurement for DL resource, the eNB
2 of the adjacent cell receives UL transmission from the UE 2 in
resource in which the UE 1 performs measurement.
[0151] In FIG. 8(a), the UE 1 receives interference from the
adjacent eNB 2, but in FIG. 8(b), the UE 1 receives interference
from the UE 2. That is, when a UE performs measurement for DL
resource, inter-cell interferences monitored by the corresponding
UE may be much different according to whether an adjacent cell
performs UL transmission or DL transmission in the same
time/frequency resource as resource in which DL measurement is
performed. In particular, a UE positioned at a cell boundary may
monitor very high interference due to a signal transmitted in UL by
a UE of an adjacent cell that is very close to the UE.
[0152] To address this issue, an eNB may limit UL resource in which
a UE (in particular, a UE positioned at a cell boundary) performs
measurement to resource that is not used for UL transmission by an
adjacent cell. In other words, the eNB may limit DL resource in
which the UE performs measurement to resource in which an adjacent
cell needs to perform UL transmission or performs DL transmission
high possibility. That is, an eNB of each cell may transmit an
index (or bitmaps of a plurality of subframes) of a DL subframe
that the eNB needs to use for DL transmission or UL transmission or
uses for DL transmission or UL transmission with very high
possibility to an eNB of an adjacent cell. In this case, an eNB may
compare a specific threshold with calculated possibility and notify
an eNB of an adjacent cell of a subframe with possibility that is
equal to or more than the specific threshold. In addition, the eNB
may also transmit index (or bitmap) information of the subframe and
information indicating use of resource at a corresponding location
to the adjacent eNB.
[0153] An eNB of a serving cell that receives index (or bitmap)
information of a DL subframe to be used for DL transmission from an
eNB of an adjacent cell may configure a UE to perform measurement
for DL resource of the serving cell in a corresponding subframe
only. In addition, an eNB of a serving cell that receives index (or
bitmap) information of a DL subframe to be used for UL transmission
from an eNB of an adjacent cell may configure a UE to perform
measurement for DL resource of the serving cell in the remaining
resources except for the corresponding resource. That is, the eNB
of the serving cell may configure a UE to perform measurement for
DL resource of the serving cell in only resource used for DL
transmission by an adjacent cell. In FIG. 8, from a viewpoint of
the UE 1, FIG. 8(a) corresponds to the aforementioned limited
resource. Likewise, the eNB of the serving cell may configure a UE
to perform measurement for DL resource of the serving cell in the
aforementioned limited resource only so as to receive stably report
of the measurement result even in a situation in which an adjacent
cell dynamically use of resource.
[0154] 2.1.2. Measurement for UL Resource
[0155] A UE may perform measurement for UL resource separately from
measurement for DL resource. This is because, during DL
transmission in UL resource, the eNB can reduce transmission power
of the eNB in order to reduce interference generated while an
adjacent eNB receives a UL signal in the same time/frequency
resource due to the DL transmission in UL resource, and
accordingly, various measurement characteristics may be largely
changed from DL measurement. Accordingly, the eNB may configure the
UE to perform measurement for UL resource separately from
measurement for DL resource, and the UE may perform separate
measurement for UL resource according to this configuration and
report the measurement to the eNB.
[0156] Likewise, in order for a UE to perform measurement for UL
resource, a reference signal transmitted in UL resource is
required. Here, a reference signal for measurement for UL may have
a form of CRS or CSI-RS used for conventional DL measurement or may
have a form of DMRS or SRS used as a reference signal for
conventional UL measurement. That is, the eNB may transmit
configuration information of a reference signal for measurement for
UL resource to the UE, and an example of the configuration of the
reference signal may include sequence information of the reference
signal, cyclic shift information of the configured reference signal
sequent, spreading code information, frequency shift information,
etc. In addition, the reference signal for measurement for UL
resource may be fixedly configured so as to be previously known to
both the eNB and the UE.
[0157] From a viewpoint of time resource, it may be impossible to
perform measurement by a UE in all UL subframes. This is because a
specific within corresponding cell coverage needs to use at least
some UL subframes for UL signal transmission to the eNB.
Accordingly, similarly to measurement for DL resource, the eNB may
configure some UL subframes as subframes in which the UE performs
measurement and command the UE to perform in the corresponding
subframe only.
[0158] In general, the measurement configuration of UL resource may
be semi-statically configured via a higher layer signal such as
radio resource control (RRC) layer, and thus in this case, the eNB
may configure the UE to perform the measurement in UL subframes to
be used for DL transmission with relatively high possibility among
UL subframes. That is, an eNB of each cell may transmit information
about at least one of offset or period of subframe of a subframe,
or an index of a UL subframe that the eNB needs to use for DL
transmission or uses for DL transmission with very high possibility
to the UE via a higher layer signal. In this case, the eNB may
compare a specific threshold with calculated possibility and notify
the UE of a subframe with possibility that is equal to or more than
the specific threshold.
[0159] However, in some situations, it may be more effective to
still use an even UL subframe that is semi-statically configured to
be used for DL transmission as a subframe for UL transmission
according to a UL/DL traffic situation. Even if the UE performs
measurement in a UL subframe to be expected to be used for UL
transmission according to a signal of the eNB, when the
corresponding UL subframe is actually used for UL transmission,
serious distortion may occur in a measurement result of the UE due
to influence of unintended interference. Thus, even in an
environment in which use of a UL subframe is dynamically changed,
the following method may be used in order to more effectively
perform measurement of a UE in a UL subframe.
[0160] 1) Operation According to Subframe Use Indicator
[0161] An eNB may indicate use (e.g., whether the corresponding UL
subframe is used for UL transmission or DL transmission) of every
UL subframe (or one or more subframes) via a physical layer signal
or a media access control (MAC) layer signal. For example, the eNB
may transmit information indicating use of every UL subframe (or
one or more subframes) in the aforementioned semi-statically
configured UL subframe, and a UE that receives the indication
information from the eNB may determine only a UL subframe, use of
which is indicated as DL transmission according to the indication
information among UL subframes, as a valid measurement target. The
indication information may be configured in an indicator form for
indicating whether use of the corresponding subframe is for DL or
UL.
[0162] 2) Operation According to Scheduling Message Reception
[0163] A UE may receive a scheduling message about UL/DL
transmission transmitted from an eNB and consider a UL subframe
that is a target of the received scheduling message as a valid
subframe as a measurement target. For example, upon receiving a
message for scheduling DL transmission in a specific subframe, the
UE may consider the corresponding UL subframe as a valid
measurement target and perform measurement. Here, the scheduling
information may be transmitted via a DL subframe or a UL subframe
used for DL.
[0164] As another example, the eNB may notify the UE of a candidate
group of UL subframes as a measurement target via a higher layer
signal such as RRC. Then, when UL transmission from the
corresponding UE is scheduled in a specific UL subframe among UL
subframes included in the candidate group, the eNB may consider
that the corresponding UL subframe is not a valid measurement
target. In other words, the UE may determine that a UL subframe in
which UL transmission is not scheduled among the candidate group of
the UL subframes as a valid measurement target and perform
measurement in the corresponding UL subframe. Here, the candidate
group of the valid UL subframes as a measurement target may include
UL subframes to be used for DL transmission by the eNB with
relatively high possibility among the aforementioned UL
subframes.
[0165] Likewise, the eNB may configure the UE to perform
measurement in a UL subframe that is actually used for DL among UL
subframes, and may further configure the UE to perform measurement
for UL resource of a serving cell only in resource that is used for
DL transmission by an adjacent cell among UL sufbrames that are
actually used for DL as described in 2.1.1. above.
[0166] As described above, RSRQ of RRM measurement metric is
defined as a ratio of RSRP and RSSI (that is, RSRQ is defined as
N.times.RSRP/(E-UTRA carrier RSSI). In this regard, in an
environment in which use of a subframe is dynamically changed, it
may be difficult to transmit a reference signal in a UL subframe
with a stable period. To address this issue, RSRQ of a UL subframe
may be derived using RSRP measured in a DL subframe only and RSSI
measured in a UL subframe only. That is, the UE may not perform
RSRP measurement in a UL subframe and may perform RSRP measurement
only in a DL subframe in which stable transmission is possible. In
addition, the UE may perform RSSI measurement in a UL subframe used
for DL transmission in order to an actual interference situation.
In other words, the UE may measure the RSRP in a DL subframe using
the method described in 2.1.1. above, measure the RSSI in a UL
subframe used for DL transmission using the method described in
2.1.2. above, and report RSRQ of a UL subframe to the eNB using the
measured RSRP and RSSI.
[0167] Like the aforementioned definition of the RSSI, since the
RSSI is a value corresponding to total power of all signals
received by the UE and can be measured using all time/frequency
resources in a valid subframe for measuring of the UE, the RSSI
less requires measurement resource than the RSRP that can be
measured in a specific resource element (RE), the above operation
may be possible. In addition, when an eNB reduces transmission
power of a reference signal compared with a DL subframe in a UL
subframe, the eNB may signal a power difference of reference
signals between a UL subframe and a UL subframe, and an UE may
reflect the power difference during RSRQ calculation in a UL
subframe. That is, since the RSRP can be measured in a DL subframe
only and the RSSI can be measured in a UL subframe only, the UE may
match transmission power of reference signals transmitted in UL and
DL subframes to the same level to calculate the RSRQ. For example,
the RSRP value measured only in the DL subframe and/or the RSSI
value measured only in the UL subframe may be corrected using a
power difference of reference signals, and then, the RSRQ may be
calculated using the corrected RSRP value and/or RSSI value.
[0168] 2.1.3. Separate Measurement for UL/DL Resources
[0169] In order to know how much a specific UE is affected by UL/DL
operations of an adjacent cell, an eNB may perform respective
separate operations and report the operations to the UE according
to cases in which the adjacent cell operates for UL and operates
for DL. For example, with regard to measurement in a DL subframe,
the eNB may divide a DL subframe into two sets and configure to
correspond to each set to a DL subframe in which an adjacent cell
performs DL transmission and UL transmission with high possibility.
As described above, an eNB of each cell may transmit an index (or
bitmaps of a plurality of subframes) of a DL subframe that the eNB
needs to use for DL transmission or UL transmission or uses for DL
transmission or UL transmission with very high possibility to an
eNB of an adjacent cell. In this case, an eNB may compare a
specific threshold with calculated possibility and notify an eNB of
an adjacent cell of a subframe with possibility that is equal to or
more than the specific threshold. In addition, the eNB may also
transmit index (or bitmap) information of the subframe and
information indicating use of resource at a corresponding location
to the adjacent eNB.
[0170] Likewise, when the eNB configures two measurement sets for a
DL subframe as a subframe in which an adjacent cell performs DL
transmission with high possibility and a subframe in which the
adjacent cell performs UL transmission with high possibility, the
eNB can easily recognize influence of a transmission direction of
the adjacent cell on the corresponding cell and can recognize a
subframe in which transmission needs to be performed. Referring
back to FIG. 8, the eNB separately notifies the UE of sets of a DL
subframe in which the operation of FIG. 8(a) is performed and a DL
subframe in which the operation of FIG. 8(b) is performed, and the
UE may perform separate measurements on the respective sets and
report measured values to the eNB. This operation can be applied to
measurement in a UL subframe used for DL transmission.
[0171] The embodiments described in 2.1.1. to 2.1.3. above can be
applied to both measurements in DL and UL resources or can be
applied to only one of measurements in DL and UL resources. That
is, any one of the aforementioned embodiments can be applied to
both measurements in DL and UL resources or two embodiments of the
aforementioned embodiments can be applied to measurements in DL and
UL resources, respectively. As an example of a combination of
embodiments, the eNB may command the UE to separately perform
measurements in DL and UL resources, and the UE may perform
measurement for DL resource only in resource that is configured as
DL resource by an adjacent cell with high possibility according to
the embodiment described in 2.1.1. above but perform measurement
for UL resource only in a subframe indicated as a valid subframe
according to reception of a subframe use indicator or a scheduling
message according to the embodiment described in 2.1.2. above. In
addition, the eNB may command the UE to separately perform
measurements in DL and UL resources and divide a DL subframe into
two sets according to a transmission direction of an adjacent cell,
and the UE may separately perform measurement for DL resource in
the respective set according to the embodiment described with
reference to 2.1.3. above and perform measurement in UL resource
only in a subframe indicated as a valid subframe according to
reception of a subframe use indicator or a scheduling message
according to the embodiment described in 2.1.2. above.
[0172] 2.2. Measurement of RSSI Including Signal of Adjacent
Cell
[0173] When an eNB may transmit separate information about an
operational direction of an adjacent cell to a UE, the UE may
measure a signal of an adjacent cell, and the eNB may recognize a
transmission direction of the adjacent cell based on the measured
value reported by the UE and separate cases in which an adjacent
cell operates for UL and operates for DL. For example, as described
above, in the case of RSRP, the UE may measure the RSRP in a DL
subframe in which a serving eNB stably performs DL transmission and
report the RSRP to an eNB, and in the case of RSSI, the UE may
measure the RSSI for each respective subframe (a DL subframe or a
DL subframe) and then report distribution information of the RSSI
measured over a plurality of pre-configured subframes to the eNB.
For example, in the case of RSSI, the UE may measure the RSSI for
each respective subframe in a UL subframe used for DL transmission
and report distribution information of the RSSI measured for a
plurality of subframes to the eNB. The distribution information of
the measured RSSI value may be reported together with the measured
RSSI value pre-reported to the eNB by the UE as the measurement
result or may be reported to the eNB instead of the measured RSSI
value pre-reported to the eNB by the UE.
[0174] An example of the distribution information may include
maximum and minimum of the RSSI. The UE may report the maximum and
minimum of the RSSI monitored for a predetermined period of time to
the eNB such that the eNB may recognize a communication state of
the corresponding UE. For example, when the maximum and minimum of
the RSSI is reported at similar levels through the RSSI
distribution information, the corresponding UE can recognize that
the corresponding UE is barely affected by a communication
direction of an adjacent cell and can perform DL transmission on
the corresponding UE in a UL frame irrespective of a transmission
direction of the adjacent cell. On the other hand, when the maximum
and minimum of the RSSI are much different, it can be derived that
the great RSSI difference is caused from UL transmission of a UE of
a cell adjacent to the corresponding UE, and preferably, the eNB
performs DL transmission on the corresponding UE using resource in
which the adjacent cell mainly performs DL transmission. That is,
when the UE reports the distribution information of the RSSI to the
eNB in a DL subframe used for DL transmission, the eNB may perform
DL transmission on the corresponding UE in a DL subframe in which
an adjacent cell mainly performs DL transmission, and when the UE
reports the distribution information of the RSSI to the eNB in a UL
subframe used for DL transmission, the eNB may perform DL
transmission on the corresponding UE in a UL subframe in which the
adjacent cell mainly performs DL transmission.
[0175] The distribution information of the RSSI may have the
following forms in addition to the maximum and the minimum.
[0176] 1) The UE may report information about a frequency at which
RSSI that is equal to or more than (or exceeds) a predetermined
threshold and/or is equal to or less than (or less than) the
predetermined threshold is measured or information about a subframe
in which the RSSI is measured to the eNB. The UE may report all the
pieces of information about the frequency and subframe of the RSSI
to the eNB. Here, the subframe information refers to information
indicating a subframe measured by the aforementioned RSSI and for
example, may include a subframe index. However, when it is not
possible to specify the corresponding subframe using only the
subframe index, the subframe information may include both a radio
frame index and a subframe index. In addition, the threshold may be
given by x % of an average RSSI value calculated in a time period
of a plurality of subframes in which the UE measures RSSIs.
[0177] 2) The UE may report an average value of measured RSSI
values that are equal to or more than (or exceeds) a predetermined
threshold and/or are equal to or less than (or less than) the
predetermined threshold to the eNB. Like in 1) above, the threshold
may be given by x % of an average RSSI value calculated in a
plurality subframe time period in which the UE measures RSSIs. In
addition, a time period for calculation of an average value of the
measured RSSI value reported to the eNB may be the same as a time
period of a plurality of subframes in which the UE measures the
RSSI.
[0178] 3) The UE may align RSSI values measured in a time period of
a plurality of subframes for measurement of the RSSIs according to
their sizes and then report measured RSSI values corresponding to
predetermined specific top and/or low x % or an average of measured
RSSI values corresponding to top and/or low x % to the eNB.
[0179] An operation in which the UE measures a signal of an
adjacent cell and reports the measured signal to the eNB, that is,
an operation in which the UE reports RSSI distribution information
for a predetermined subframe period to the eNB can be applied to
both measurements for DL and UL resources or can be applied to only
one of DL and UL resources. In addition, a combination of the
operation and the method described in 2.1. above can be used.
[0180] The aforementioned method of reporting the RSSI distribution
information can be performed by directly reporting the RSSI
distribution information to the eNB or by reporting RSRQ
distribution information acquired via combination with a measured
RSRP value to the eNB.
[0181] 3. Overview of Apparatus to which the Present Invention is
Applicable
[0182] FIG. 9 is a block diagram of a wireless communication
apparatus according to an embodiment of the present invention.
[0183] Referring to FIG. 9, a wireless communication system
includes a BS 90 and a plurality of UEs 100 positioned within a
region of the BS 90.
[0184] The BS 90 includes a processor 91, a memory 92, and a radio
frequency (RF) unit 93. The processor 91 embodies the proposed
functions, processes, and/or methods. Layers of a wireless
interface protocol may be embodied by the processor 91. The memory
92 is connected to the processor 91 and stores various pieces of
information for driving the processor 91. The RF unit 93 is
connected to the processor 91 and transmits and/or receives a radio
signal.
[0185] The UE 100 includes a processor 101, a memory 102, and an RF
unit 103. The processor 101 embodies the proposed functions,
processes, and/or methods. Layers of a wireless interface protocol
may be embodied by the processor 101. The memory 102 is connected
to the processor 101 and stores various pieces of information for
driving the processor 101. The RF unit 103 is connected to the
processor 101 and transmits and/or receives a radio signal.
[0186] The memories 92 and 102 may be disposed within or outside
the processors 91 and 101 and may be connected to the processors 91
and 101 via various means. In addition, the BS 90 and/or the UE 100
may have a single antenna or multiple antennas.
[0187] The embodiments of the present invention described above are
combinations of elements and features of the present invention. The
elements or features may be considered selective unless otherwise
mentioned. Each element or feature may be practiced without being
combined with other elements or features. Further, an embodiment of
the present invention may be constructed by combining parts of the
elements and/or features. Operation orders described in embodiments
of the present invention may be rearranged. Some constructions of
any one embodiment may be included in another embodiment and may be
replaced with corresponding constructions of another embodiment. It
is obvious to those skilled in the art that claims that are not
explicitly cited in each other in the appended claims may be
presented in combination as an embodiment of the present invention
or included as a new claim by a subsequent amendment after the
application is filed.
[0188] The embodiments of the present invention may be achieved by
various means, for example, hardware, firmware, software, or a
combination thereof. In a hardware configuration, the methods
according to exemplary embodiments of the present invention may be
achieved by one or more application specific integrated circuits
(ASICs), digital signal processors (DSPs), digital signal
processing devices (DSPDs), programmable logic devices (PLDs),
field programmable gate arrays (FPGAs), processors, controllers,
microcontrollers, microprocessors, etc.
[0189] In a firmware or software configuration, an embodiment of
the present invention may be implemented in the form of a module, a
procedure, a function, etc. Software code may be stored in a memory
unit and executed by a processor. The memory unit is located at the
interior or exterior of the processor and may transmit and receive
data to and from the processor via various known means.
[0190] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
INDUSTRIAL APPLICABILITY
[0191] The data transmission/reception method in a wireless access
system according to the present invention has been described in
terms of an example applied to a 3rd generation partnership project
long term evolution (3GPP LTE) system but can be applied to various
wireless access systems in addition to the 3GPP LTE system.
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